In the past, attempts have been made to provide aircraft with both aerodynamic and aerostatic lift. Thus rigid and non-rigid gas-filled airships, which are normally lighter-than-air, are capable of taking off even though overloaded to the point that they are heavier-than-air. Such air vehicles, however, have been generally in the form of prolate ellipsoids of approximately circular cross-section, and the aerodynamic lift imparted to such air vehicles is minimal when compared with a conventional airfoil with the same planform area.
Since the lift in conventional airships is primarily aerostatic brought about by the hull being filled with lighter than air gas, such as helium, their cargo-carrying capability is limited by the volume of the gas envelope, and the total lift at best corresponds to little more than the weight of the air displaced by the gas envelope. Furthermore, in conventional cargo-carrying airships problems are encountered in loading and unloading the cargo and of dispersing concentrated loads.
Lighter-than-air airships are incapable of taxiing on their landing fields, and take-off and landing procedures are consequently very comply, requiring costly equipment and large number of persons in ground crews. On the other hand, conventional cargo airplanes, while they are capable of taxiing, have high take-off and landing speeds.
In GB-A-1,245,432 there is disclosed an aircraft which takes advantage of both the lift provided by a lighter-than-air gas and aerodynamic lift. The aircraft has an enclosed aluminium hull containing a lighter-than-air gas and which is delta-shaped in plan form and has an ellipse-like cross-section throughout substantially all of its length. The delta wing shape and low aspect ratio of the design provides a high cargo capacity as well as good aerodynamic performance. The aluminium hull is inflated with helium and cargo and fuel compartments are provided inside the hull suspended by numerous high-strength steel cables which distribute the concentrated load of the cargo and fuel compartments over the large area of the upper shell of the body. The propulsion system in arranged at the rear of the aircraft so that the propulsion system is effectively behind the drag producing system. As a result, the momentum loss of the flow due to the deceleration of the drag system is compensated by the accelerating action of the propulsion system, thus restoring the original velocity of the air with respect to the aircraft. Because of its excess gross weight, and because it is provided with landing gear, the aircraft is capable or taxiing on the ground in the same manner as a conventional multi-engine aircraft.
The aircraft described in GB-A-1,245,432 is more akin in design to an airplane than to an airship, the majority of the lift being provided by the aerodynamic delta shape of the hull. The hull is formed as a rigid framework of aluminium panels and the load compartment is housed within the hull. The width of the aircraft at its stern is about 75% of the length of the aircraft. Thus for an aircraft having a length of about 305 m, the width at the stern of the aircraft will be about 230 m. This places severe limitations where the aircraft can take off and land because of the need to have a flat runway capable of catering for such a wide aircraft.